Giant magnetoresistance (GMR) elements formed of multilayer films, i.e., ferromagnetic layers and non-magnetic layers, and tunneling magnetoresistance (TMR) elements using insulating layers (tunnel barrier layers or barrier layers) as non-magnetic layers are known. Generally, TMR elements have higher element resistances than GMR elements and magnetoresistance (MR) ratios of TMR elements are higher than MR ratios of GMR elements. For this reason, TMR elements have attracted attention as elements for magnetic sensors, high frequency components, magnetic heads, and nonvolatile random access memories (MRAMs).
In an MRAM, data is read and written using characteristics in which an element resistance of a TMR element changes when magnetization directions of two ferromagnetic layers sandwiching an insulating layer change. As writing methods for MRAMs, a method in which writing (magnetization reversal) is performed using a magnetic field produced by a current and a method in which writing (magnetization reversal) is performed using a spin transfer torque (STT) occurring when a current flows in a lamination direction of a magnetoresistance effect element are known. Magnetization reversals of TMR elements using an STT are efficient from the viewpoint of energy efficiency, but an inversion current density to cause magnetization reversal is large. In order to improve the durability of TMR elements, it is desirable that reversal current densities be low. This applies to GMR elements.
Since a reversal current density due to an STT is proportional to a volume of a ferromagnetic material constituting a ferromagnetic layer, it has been attempted to reduce the reversal current density by reducing the volume of the ferromagnetic material. However, on the other hand, there is a problem that a magnetic recording holding time is shortened when the volume of the ferromagnetic material is reduced. This is because the energy of the ferromagnetic material depends on the magnetically anisotropic energy and a volume of the ferromagnetic material and thus the energy of the ferromagnetic material weakens and it becomes impossible to maintain a ferromagnetic magnetic order when the volume of the ferromagnetic material is decreased, and as a result, thermal disturbance due to heat from the outside is caused. Therefore, in order to maintain a magnetic recording holding time, resilience and high thermal stability in response to thermal disturbance are also required, but in a method using an STT, it is difficult to reduce a reversal current density without reducing the volume of a ferromagnetic material.
Therefore, in recent years, as means for reducing a reverse current with a mechanism different from an STT, attention has been focused on magnetization reversal using a pure spin current generated by a spin orbit interaction (for example, Non-Patent Literatures 1 to 3). A pure spin current generated by spin orbit interaction induces a spin orbital torque (SOT) and magnetization reversal is caused by the SOT. Furthermore, a pure spin current generated by a Rashba effect at an interface between different materials also causes magnetization reversal due to the same SOT. However, these mechanisms have not yet been clarified. A pure spin current is generated when the same number of electrons with an upward spin and electrons with a downward spin flow in opposite directions and flows of charge cancel each other out. For this reason, a current flowing through a magnetoresistance effect element is zero and realization of a magnetoresistance effect element with a small reversal current density would be expected, but it is currently reported in Non-Patent Literature 1 or the like that an reversal current density due to an SOT is substantially the same as an reversal current density due to an STT.